Dovetail structure of fan

ABSTRACT

The invention provides a dovetail structure of a fan which attaches the fan  20  having an inlet hub diameter smaller than an outlet hub diameter to a portion around a discoid disc  10  rotationally driven by a turbine. The disc  10  has a plurality of main dovetail grooves  12  extending in parallel to an axis  1  of a rotation axis from a leading edge to a trailing edge thereof. The fan  20  has a main dovetail portion  22  fitted to the main dovetail groove  12,  and a sub engagement portion  24  for supporting a front centrifugal force. Further, the dovetail structure is provided with a spin cone  30  engaging with the sub engagement portion  24  so as to be capable of transmitting the front centrifugal force to the disc  10.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to a turbofan engine which has a highbypass ratio and can achieve a good mileage and a low noise, and moreparticularly to a dovetail structure of a fan in which an inlet hubdiameter is smaller than an outlet hub diameter.

2. Description of the Related Art

FIG. 1 is a schematic view of an aircraft engine 51 (a turbojet engine).As shown in this drawing, the turbojet engine is provided with a fan 52taking in an air, a compressor 53 compressing the intake air, a burningdevice 54 burning a fuel by the compressed air, a turbine 55 driving thefan 52 and the compressor 53 on the basis of a combustion gas of theburning device 54, an afterburner 56 afterburning for increasing athrust, and the like.

The afterburner 56 is constituted by a flame holder 57 having atriangular cross section or the like and forming a circulating region ina downstream side so as to achieve a flame holding, a fuel nozzle 58 forjetting out a fuel, a spark plug 59 and the like, jets out from anexhaust nozzle 62 through an inner side of a liner 61 in an inner sideof an after duct 60, and increases a thrust.

In the turbojet engine mentioned above, a structure in which the fan 52taking in the air is enlarged in size, and a bypass ratio is enlarged iscalled “turbofan engine”. The bypass ratio corresponds to a flow ratio(bypass flow/core flow) of a bypass flow bypassing a core engine (thecompressor 53, the burning device 54 and the turbine 55 mentioned above)with respect an air flow (a core flow) flowing into the core engine. Thelarger the bypass ratio is, the more the flow rate of the exhaust jet isreduced, so that there is obtained an effect of lowering a noise and aspecific fuel consumption.

However, in the turbo engine mentioned above, if the bypass ratio isenlarged, a fan first stage rotor blade (a fan blade in the front row)and an inner diameter of a casing surrounding it become enlarged, andthere is a problem that a weight of the engine is increased.

In other words, since a fan first stage rotor blade 52a having astructure embedded in a spinner 63 of the turbofan engine has anembedded structure, a certain degree of hub/tip ratio (inlet hubdiameter/tip diameter shown in FIG. 2: normally about 0.3) is necessary,and a fan inlet area becomes narrower at an area corresponding to theinlet hub diameter.

Accordingly, if it is intended to increase the bypass ratio in order toachieve the good mileage and the low noise, the fan diameter and theinlet hub diameter become further larger, and the weight of the engineis increased.

Then, in order to solve the problem, the same applicant as that of thepresent invention has already proposed “turbofan engine” in patentdocument 1.

The turbofan engine is provided with a fan first stage rotor blade 65for taking in an air, and a spinner 64 rotationally driving the fanfirst stage rotor blade, as shown in FIG. 3, and the spinner has aspiral blade 66 extending spirally to an outer side in a radialdirection from an axis thereof and sucking the air from a front surfaceof the spinner so as to supply to the fan first stage rotor blade.

In this case, reference numerals 67 and 67′ denote a casing innerdiameter, and reference numeral 68 denotes an inflow air flow.

In accordance with the structure of the patent document 1, since thespinner 64 has the spiral blade 66 extending spirally to the outer sidein the radial direction from the axis thereof and sucking the air fromthe front surface of the spinner so as to supply to the fan first stagerotor blade 65, it is possible to suck the air from the front surface ofthe spinner corresponding to the inlet hub diameter so as to compressthe air and supply to the fan first stage rotor blade 65.

Therefore, since an entire area in the front side of the engine becomesthe air inflow area of the fan first stage rotor blade 65, it ispossible to make the fan diameter small, and it is possible to reducethe engine weight.

Further, since the fan first stage rotor blade 65 and the spiral blade66 of the turbofan engine mentioned above are integrally coupled, it ispossible to connect the respective blade surfaces smoothly, and it ispossible to suck and compress the air efficiently. Hereinafter, the fanin which the fan first stage rotor blade 65 and the spiral blade 66 areintegrally formed, the air can be sucked from the front surface of thespinner, and the substantial hub/tip ratio can be set to 0 is called as“zero hub tip ratio fan”.

Patent Document 1: Japanese Unexamined Patent Publication No.2004-27854, “TURBOFAN ENGINE”

Patent Document 2: U.S. Pat. No. 6,764,282, “BLADE FOR TURBINE ENGINE”

It is necessary to attach the fan blade of the turbofan engine to aportion around a discoid disc (or spinner) rotationally driven by aturbine. Accordingly, in conventional, there has been generally employeda dovetail structure in which a dovetail portion extending in alongitudinal direction is provided in a root portion of the fan blade,and the dovetail portion is fitted to a dovetail groove formed aroundthe disc.

In the conventional dovetail structure mentioned above, the dovetailportion and the dovetail groove are provided in parallel to a rotationaxis Z-Z of the disc, thereby preventing a centrifugal force applied tothe fan blade from generating a component force in an axial direction.Hereinafter, this structure is called as “parallel dovetail structure”.

However, in the case that a diameter change in an inner side of adonut-shaped flow path to which the fan blade is attached is large, ifthe parallel dovetail structure is employed, it is necessary to make adiameter of the dovetail portion and the dovetail groove equal to orsmaller than a minimum diameter of the flow path, and there is a riskthat a stress generated in the dovetail portion and the dovetail groovebecomes too large.

Accordingly, there has been proposed a dovetail structure in which thedovetail portion and the dovetail groove shown in FIG. 4 are sloped withrespect to the rotation axis (for example, patent document 2). In thisdrawing, reference numeral 71 denotes a disc, reference numeral 73denotes a blade, reference numeral 77 denotes a dovetail, and referencenumeral 79 denotes a tab.

Hereinafter, this structure is called as “slope dovetail structure”.

However, in the case of the zero hub tip ratio fan mentioned above,since the hub/tip ratio is between 0 and 0.35, and the diameter of theinner side of the donut-shaped flow path to which the zero hub tip ratiofan is attached is zero or close to zero, there is a problem that theparallel dovetail structure can not be essentially applied.

Further, even in the case that the slope dovetail structure is applied,it is impossible to support the centrifugal force of the front sideportion (the portion corresponding to the spiral blade mentioned above)of the zero hub tip ratio fan by the disc (or the spinner).

Further, in the case that the slope dovetail structure is applied to thezero hub tip ratio fan, since the component force in the axial directionof the centrifugal force applied to the fan blade is large, there is arisk that the generated stress becomes too large in the structure havinga small shear area such as the tab disclosed in the patent document 2.

SUMMARY OF THE INVENTION

The present invention is made for the purpose of solving the problemsmentioned above. In other words, an object of the present invention isto provide a dovetail structure of a fan which can securely attach a fanhaving an inlet hub diameter smaller than an outer hub diameter to aportion around a disc rotationally driven by a turbine, and can securelysupport component forces in a radial direction and an axial direction ofa centrifugal force applied to the fan having the inlet hub diametersmaller than the outlet hub diameter by a low stress.

In accordance with the present invention, there is provided a dovetailstructure of a fan which attaches a fan having an inlet hub diametersmaller than an outlet hub diameter to a portion around a discoid discrotationally driven by a turbine,

wherein the disc has a plurality of main dovetail grooves extending inparallel to an axis of a rotation axis from a leading edge to a trailingedge thereof, and spaced at a fixed angle in a peripheral direction,

wherein the fan has a main dovetail portion fitted to the main dovetailgroove so as to be capable of transmitting a rear centrifugal forceapplied to a portion from an intermediate portion to a trailing edge,and a sub engagement portion for supporting a front centrifugal forceapplied to a portion from a leading edge to the intermediate portion,and

wherein the dovetail structure is provided with a spin cone engagingwith the sub engagement portion so as to be capable of transmitting thefront centrifugal force to the disc.

In accordance with a preferable aspect of the present invention, the fanis constituted by a zero hub ratio fan which is capable of sucking anair close to a center of rotation, and in which a substantial inlet hubdiameter is zero or close to zero, and a hub/tip ratio is between 0 and0.35.

Further, the sub engagement portion is constituted by a projectionportion which is provided in an inner end portion of a forward end ofthe fan, and has an outer peripheral surface spaced at a fixed distanceR from the axis of the rotating shaft, and

the spin cone has a concave groove having an inner peripheral surfacefitted to an outer peripheral surface of the projection portion, and afaucet portion fitted to a cylindrical inner surface provided in thedisc.

Further, in accordance with the other preferable embodiment, the subengagement portion is constituted by a plurality of slope dovetailportions extending at a fixed angle with respect to the axis of therotating shaft from the leading edge of the fan to the intermediateportion, and spaced at a fixed angle in a peripheral direction, and

the spin cone has a plurality of slope dovetail grooves fitted to theslope dovetail portions, and a faucet portion fitted to the cylindricalinner surface provided in the disc.

Further, in accordance with the other preferable embodiment, the subengagement portion has a plurality of parallel dovetail portionsextending in parallel to the axis of the rotating shaft from the leadingedge of the fan to the intermediate portion, and spaced at a fixed anglein a peripheral direction, and

the spin cone has a plurality of parallel dovetail grooves fitted to theparallel dovetail portions, and a faucet portion fitted to thecylindrical inner surface provided in the disc.

Further, in accordance with the other preferable embodiment, the subengagement portion is constituted by a plurality of expanded portionsextending from the leading edge of the fan to the intermediate portionand spaced at a fixed angle in a peripheral direction, and

the spin cone has a plurality of fitting grooves fitted to a front loweredge of the fan in an upper portion than the expanded portions, and afaucet portion fitted to the cylindrical inner surface provided in thedisc.

In accordance with the structure of the present invention mentionedabove, since the disc has the main dovetail groove extending in parallelto the axis of the rotation axis from the leading edge to the trailingedge, and the fan having the inlet hub diameter smaller than the outlethub diameter has the main dovetail portion extending at the same angleas the angle of the dovetail groove and capable of being fitted to thedovetail groove, it is possible to securely attach the fan to theportion around the disc, and it is possible to securely transmit therear centrifugal force applied to the fan to the disc via the maindovetail portion and the main dovetail groove.

Further, since the main dovetail portion and the main dovetail grooveextend in parallel to the axis of the rotation axis, it is possible toset a sufficient long main dovetail groove capable of transmitting therear centrifugal force applied to the portion from the intermediateportion to the trailing edge, even in the case of attaching the fanhaving the inlet hub diameter smaller than the outlet hub diameter, andit is possible to sufficiently suppress the stress generated in the maindovetail portion and the main dovetail groove.

Further, since the fan has the sub engagement portion for supporting thefront centrifugal force applied to the portion from the leading edge tothe intermediate portion, and is provided with the spin cone engagingwith the sub engagement portion so as to be capable of transmitting thefront centrifugal force to the disc, it is possible to securely supportthe front centrifugal force applied to the portion having the small hubdiameter of the fan in which the inlet hub diameter is smaller than theoutlet hub diameter, via the spin cone so as to be capable of securelytransmitting to the disc.

Further, since the rear centrifugal force applied to the portion fromthe intermediate portion to the trailing edge is transmitted to the discby the main dovetail groove and the main dovetail portion extending inparallel to the axis of the rotating shaft, it is possible to make thecomponent force along the main dovetail groove of the centrifugal forceapplied to the fan in which the inlet hub diameter is smaller than theoutlet hub diameter small, and it is possible to securely support thecomponent force by the low stress on the basis of the retainer structurehaving the same structure as the conventional one.

The other objects and advantageous features of the present inventionwill be apparent from the following description with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a conventional turbofan engine;

FIG. 2 is an explanatory view of a hub/tip ratio;

FIG. 3 is a schematic view of “turbofan engine” in patent document 1;

FIG. 4 is a schematic view of “slope dovetail structure” in patentdocument 2;

FIG. 5 is a transverse cross sectional view of a fan provided with adovetail structure in accordance with a first embodiment of the presentinvention;

FIGS. 6A, 6B, 6C and 6D are partly cross sectional views of FIG. 5;

FIG. 7 is a view of a second embodiment of the dovetail structure inaccordance with the present invention;

FIGS. 8A, 8B and 8C are partly perspective views and a partly crosssectional view of FIG. 7;

FIG. 9 is a view of a third embodiment of the dovetail structure inaccordance with the present invention;

FIG. 10 is a partly perspective view of FIG. 9;

FIG. 11 is a view of a fourth embodiment of the dovetail structure inaccordance with the present invention; and

FIGS. 12A and 12B are partly perspective views of FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given below of a preferable embodiment inaccordance with the present invention with reference to the accompanyingdrawings. In this case, in each of the drawings, the same referencenumerals are attached to a common portion, and an overlappingdescription will be omitted.

FIG. 5 is a transverse cross sectional view of a fan provided with adovetail structure in accordance with a first embodiment of the presentinvention, and shows only an upper side of an axis 1 of a rotatingshaft.

Further, FIGS. 6A, 6B, 6C and 6D are partly cross sectional views ofFIG. 5, and are respectively cross sectional views along a line A-A, aline B-B, a line C-C and a line D-D.

A dovetail structure in accordance with the present invention isstructured such that a fan in which an inlet hub diameter is smallerthan an outlet hub diameter is attached to a portion around a discoiddisc 10 rotationally driven by a turbine (not shown).

Further, in this embodiment, the fan is constituted by a zero hub tipratio fan which can suck an area close to a center of rotation, and inwhich a substantial inlet hub diameter is zero or close to zero, and ahub/tip ratio is between 0 and 0.35.

In this case, in FIG. 5, reference numeral 1 denotes an axis of arotating shaft of a disc 10 and the zero hub tip ratio fan 20, referencenumeral 2 denotes an air flow path, reference numeral 3 denotes an innerperipheral surface of the air flow path, reference numeral 4 denotes abearing rotatably supporting the disc 10, and reference numeral 5denotes a flow of an inflow air.

The zero hub tip ratio fan 20 is formed such that a fan first stagerotor blade 20 a for taking in the air and a spiral blade 20 b suckingthe air from the portion close to the center of rotation so as tocompress and supply to the fan first stage rotor blade are integrallycoupled, and respective blade surfaces are smoothly connected. In thiscase, the substantial hub/tip ratio of the zero hub tip ratio fan 20 isnot 0, but can be set to 0.

In FIGS. 5, 6A, 6B, 6C and 6D, the disc 10 has a plurality of (forexample, eighteen in this embodiment) main dovetail grooves 12 spaced ata fixed angle (for example, 20 degree in this embodiment) in aperipheral direction. Further, the main dovetail grooves 12 extend inparallel to the axis 1 of the rotating shaft from a leading edge 10 a toa trailing edge 10 b of the disc 10.

The zero hub tip ratio fan 20 has a main dovetail portion 22 in an innerend thereof. The main dovetail portion 22 extends in parallel to theaxis 1 of the rotating shaft in the same manner as the main dovetailgroove 12 of the disc 10, and is structured such as to be capable ofbeing fitted to the main dovetail groove 12.

It is preferable that the main dovetail portion 22 is provided at aposition corresponding to a fan first stage rotor blade 20 a, and isstructured such as to be capable of transmitting a rear centrifugalforce applied to a portion from an intermediate portion to a trailingedge of the fan to the disc 10.

The zero hub tip ratio fan 20 further has a sub engagement portion 24for supporting a front centrifugal force applied to a portion from aleading edge to the intermediate portion of the fan. The sub engagementportion 24 is preferably provided at a position corresponding to aspiral blade 20 b. In this case, reference numeral 26 in this drawingdenotes a platform portion constituting the inner peripheral surface 3of the air flow path 2 of the zero hub tip ratio fan 20.

In FIG. 5, the dovetail structure in accordance with the presentinvention is further provided with a spin cone 30 capable of being fixedto the disc 10 by a coupling bracket 15 in a forward side (a left sidein the drawing) of the zero hub tip ratio fan 20. The spin cone 30engages with the sub engagement portion 24 of the zero hub tip ratio fan20 and has a function of transmitting a front centrifugal force appliedto the portion from the leading edge to the intermediate portion of thefan to the disc 10.

In the first embodiment in FIG. 5, the sub engagement portion 24 isconstituted by a projection portion 25 which is provided in an inner endportion of a forward end of the zero hub tip ratio fan 20, and has anouter peripheral surface 25 a spaced at a fixed distance R from the axis1 of the rotating shaft.

Further, in this embodiment, the spin cone 30 has a concave groove 31having an inner peripheral surface fitted to the outer peripheralsurface 25 a of the projection portion 25, and a faucet portion 37fitted to a cylindrical inner surface 10 c provided in the disc 10.

In this embodiment, the spin cone 30 has a cone head 36 attached to aleading end thereof by a coupling bracket 35.

In the case of the zero hub tip ratio fan 20 in which a substantialinlet hub diameter is zero or close to zero, a flow path diameter of theinner peripheral surface 3 of the air flow path 2 is largely changedfrom zero or a small diameter close to zero to a large diameter reachingthree times or more (about three times in this embodiment) thereof.Accordingly, a diameter of outer peripheral surface 25 a of theprojection portion 25 becomes equal to or less than one third of themaximum diameter of the mounting portion of the main dovetail portion22.

Further, the front centrifugal force applied to the portion from theleading edge to the intermediate portion of the fan corresponds to acentrifugal force applied to the spiral blade 20 b positioned in anouter side thereof, and is smaller in comparison with a rear centrifugalforce applied to the portion from the intermediate portion to thetrailing edge of the fan.

Accordingly, it is possible to support the front centrifugal force onthe basis of the engagement between the projection portion 25 providedin the inner end portion of the forward end and the concave groove 31 ofthe spin cone 30.

In accordance with the structure mentioned above, since the disc 10 hasthe main dovetail groove 12 extending in parallel to the axis 1 of therotating shaft from the leading edge 10 a to the trailing edge 10 b, andthe zero hub tip ratio fan 20 has the main dovetail portion 22 which isfitted to the main dovetail groove and can transmit the rear centrifugalforce applied to the portion from the intermediate portion to thetrailing edge, it is possible to securely attach the zero hub tip ratiofan 20 to the portion around the disc 10, and it is possible to securelytransmit the rear centrifugal force applied to the zero hub tip ratiofan 20 to the disc 10 via the main dovetail portion 22 and the maindovetail groove 12.

Further, since the main dovetail portion 22 and the main dovetail groove12 extend in parallel to the axis 1 of the rotating shaft, it ispossible to set the sufficiently long main dovetail groove which cantransmit the rear centrifugal force applied to the portion from theintermediate portion to the trailing edge, even in the case of attachingthe zero hub tip ratio fan in which the substantial inlet hub diameteris zero or close to zero, and it is possible to suppress the stressgenerated in the main dovetail portion 22 and the main dovetail groove12 sufficiently small.

Further, since the zero hub tip ratio fan 20 has the sub engagementportion 24 (the projection portion 25 in this embodiment) for supportingthe front centrifugal force applied to the portion from the leading edgeto the intermediate portion, further has the concave groove 31 and thefaucet portion 37 in this embodiment, and is provided with the spin cone30 engaging with the sub engagement portion 24 so as to be capable oftransmitting the front centrifugal force to the disc 10, it is possibleto securely support the front centrifugal force applied to the portionin which the hub diameter of the zero hub tip ratio fan is zero or closeto zero via the concave groove 31 and the faucet portion 37 of the spincone 30 so as to securely transmit to the disc 10.

Further, since the rear centrifugal force applied to the portion fromthe intermediate portion to the trailing edge is transmitted to the disc10 by the main dovetail groove 12 and the main dovetail portion 22extending in parallel to the axis of the rotating shaft, it is possibleto make the component force along the main dovetail groove of thecentrifugal force applied to the zero hub tip ratio fan 20 small, and itis possible to securely support the component force by the low stress onthe basis of the retainer structure having the same structure as theconventional one.

In FIG. 5, the main dovetail portion 22 of the zero hub tip ratio fan 20has a vertical rear surface 23 which is orthogonal to the main dovetailgroove 12, in a rearward end thereof.

Further, the dovetail structure in accordance with the present inventionhas a rear retainer 16 fixed to a rear end surface (a rear edge 10 b) ofthe disc 10 by a coupling bracket (for example, a bolt and a nut) (notshown).

The rear retainer 16 is structured such that a front surface thereof isclosely attached to the vertical rear surface 23 so as to prevent themain dovetail portion 22 from moving backward.

In accordance with this structure, it is possible to make a surfacepressure of a contact surface of the rear retainer substantiallyconstant, and it is possible to reduce the internal stress generated inthe rear retainer.

In this case, the fixing means in the axial direction of the zero hubtip ratio fan 20 is not limited to the vertical rear surface 23 and therear retainer 16 mentioned above, but may employ the other well-knownmeans singly or together.

FIG. 7 is a view showing a second embodiment of the dovetail structurein accordance with the present invention. Further, FIG. 8A is a partlyperspective view of a fan front portion, FIG. 8B is a perspective viewalong a line B-B in FIG. 7, and FIG. 8C is a partly cross sectional viewalong a line C-C in FIG. 7.

In this embodiment, the sub engagement portion 24 is constituted by aplurality of slope dovetail portions 27. The slope dovetail portions 27extend at a fixed angle Θ with respect to the axis 1 of the rotatingshaft from the leading edge to the intermediate portion of the zero hubtip ratio fan 20, and are spaced at a fixed angle (for example, 20degree in this embodiment) in a peripheral direction.

The fixed angle Θ corresponds to an angle in which a forward side isclose to the axis 1 and a rearward side is away from the axis 1, andpreferably corresponds to an angle along the inner peripheral surface 3of the air flow path 2. In this case, the angle Θ is about 40 degree inthis embodiment.

Further, in this embodiment, the spin cone 30 has a plurality of slopedovetail grooves 32 fitted to the slope dovetail portions 27, a faucetportion 37 fitted to a cylindrical inner surface 10 c provided in thedisc 10, and a faucet portion 38 fitted to a cylindrical inner surface10 d provided in an outer side of the disc 10.

The other structures are the same as those of the first embodiment.

In accordance with the structure mentioned above, since the zero hub tipratio fan 20 has the sub engagement portion 24 (the slope dovetailportion 27 in this embodiment) for supporting the front centrifugalforce applied to the portion from the leading edge to the intermediateportion, further has the slope dovetail groove 32 and the faucetportions 37 and 38 in this embodiment, and is provided with the spincone 30 engaging with the sub engagement portion 24 so as to be capableof transmitting the front centrifugal force to the disc 10, it ispossible to securely support the front centrifugal force applied to theportion in which the hub diameter of the zero hub tip ratio fan is zeroor close to zero via the slope dovetail groove 32 and the faucetportions 37 and 38 of the spine cone 30 so as to be capable of securelytransmitting to the disc 10.

The other operations and effects are the same as those of the firstembodiment.

FIG. 9 is a view of a third embodiment of the dovetail structure inaccordance with the present invention. Further, FIG. 10 is a partlyperspective view of a fan front portion of FIG. 9.

In this embodiment, the sub engagement portion 24 is constituted by aplurality of parallel dovetail portions 28. The parallel dovetailportions 28 extend in parallel to the axis 1 of the rotating shaft fromthe leading edge to the intermediate portion of the zero hub tip ratiofan 20, and are spaced at a fixed angle (for example, 20 degree in thisembodiment) in the peripheral direction.

A centrifugal force (a front centrifugal force) applied to the paralleldovetail portion 28 corresponds to a centrifugal force applied to thespiral blade 20 b positioned in an outer thereof, and is smaller incomparison with a centrifugal force of the fan first stage rotor blade20 a applied to the main dovetail portion 22.

Accordingly, it is preferable that a size of the parallel dovetailportion 28 is made sufficiently smaller than a size of the main dovetailportion 22.

Further, in this embodiment, the spin cone 30 has a plurality ofparallel dovetail grooves 33 fitted to the parallel dovetail portion 28,and a faucet portion 37 fitted to a cylindrical inner surface 10 cprovided in the disc 10.

The other structures are the same as those of the first embodiment.

In accordance with the structure mentioned above, since the zero hub tipratio fan 20 has the sub engagement portion 24 (the parallel dovetailportion 28 in this embodiment) for supporting the front centrifugalforce applied to the portion from the leading edge to the intermediateportion, further has the parallel dovetail groove 33 and the faucetportion 37 in this embodiment, and is provided with the spin cone 30engaging with the sub engagement portion 24 so as to be capable oftransmitting the front centrifugal force to the disc 10, it is possibleto securely support the front centrifugal force applied to the portionin which the hub diameter of the zero hub tip ratio fan is zero or closeto zero via the parallel dovetail groove 33 and the faucet portion 37 ofthe spin cone 30 so as to be capable of securely transmitting to thedisc 10.

The other operations and effects are the same as those of the firstembodiment.

FIG. 11 is a view of a fourth embodiment of the dovetail structure inaccordance with the present invention, FIG. 12A is a partly perspectiveview of the fan front portion, and FIG. 12B is a partly perspective viewof the spin cone.

In this embodiment, the sub engagement portion 24 is constituted by aplurality of expanded portions 29. The expanded portions 29 extend tothe intermediate portion from the leading edge of the zero hub tip ratiofan 20, and are spaced at a fixed angle (for example, 20 degree in thisembodiment) in the peripheral direction. A width in the peripheraldirection of the expanded portion 29 is preferably formed thicker than afront lower edge of the fan.

In this case, “structure in which the width in the peripheral directionof the expanded portion 29 is formed thicker than the front lower edgeof the fan” is not essential in the case that the front centrifugalforce applied to the intermediate portion from the leading edge of thezero hub tip ratio fan 20 is sufficiently low. In other words, it is notessential to employ a structure in which a thickness is increased and aload is transmitted.

Further, in this embodiment, the spin cone 30 has a plurality of fittinggrooves 34 fitted to the front lower edge of the fan in the upperportion than the expanded portion 29, a faucet portion 37 fitted to thecylindrical inner surface 10 c provided in the disc 10, and a faucetportion 38 fitted to the cylindrical inner surface 10 d provided in anouter side of the disc 10.

The other structures are the same as those of the first embodiment.

In accordance with the structure mentioned above, since the zero hub tipratio fan 20 has the sub engagement portion 24 (the expanded portion 29in this embodiment) for supporting the front centrifugal force appliedto the portion from the leading edge to the intermediate portion,further has the fitting groove 34 and the faucet portions 37 and 38 inthis embodiment, and is provided with the spin cone 30 engaging with thesub engagement portion 24 so as to be capable of transmitting the frontcentrifugal force to the disc 10, it is possible to securely support thefront centrifugal force applied to the portion in which the hub diameterof the zero hub tip ratio fan is zero or close to zero via the fittinggroove 34 and the faucet portions 37 and 38 of the spin cone 30 so as tobe capable of securely transmitting to the disc 10.

The other operations and effects are the same as those of the firstembodiment.

In the fourth embodiment mentioned above, (1) it is possible to transmitthe front centrifugal force applied to the portion in which the hubdiameter of the zero hub tip ratio fan is zero or close to zero, and thehub/tip ratio is between 0 and 0.35, to the disc 10 on the basis of thefitting between the main dovetail portion 22 and the main dovetailgroove 12, and (2) it is possible to make the size of the expandedportion 29 small or substantially omit the expanded portion 29, as faras the front lower edge of the fan in the upper portion than theexpanded portion 29 and the fitting groove 34 are fitted so as tosuppress the vibration of the fan.

In this case, it goes without saying that the present invention is notlimited to the embodiments mentioned above, but can be variouslymodified in a range within the scope of the present invention.

1. A dovetail structure of a fan which attaches the fan having an inlethub diameter smaller than an outlet hub diameter to a portion around adiscoid disc rotationally driven by a turbine, wherein the disc has aplurality of main dovetail grooves extending in parallel to an axis of arotation axis from a leading edge to a trailing edge thereof, and spacedat a fixed angle in a peripheral direction, wherein the fan has a maindovetail portion fitted to the main dovetail groove so as to be capableof transmitting a rear centrifugal force applied to a portion from anintermediate portion to a trailing edge, and a sub engagement portionfor supporting a front centrifugal force applied to a portion from aleading edge to the intermediate portion, and wherein the dovetailstructure is provided with a spin cone engaging with the sub engagementportion so as to be capable of transmitting the front centrifugal forceto the disc.
 2. The dovetail structure of the fan as claimed in claim 1,wherein the fan is constituted by a zero hub ratio fan which is capableof sucking an air close to a center of rotation, and in which asubstantial inlet hub diameter is zero or close to zero, and a hub/tipratio is between 0 and 0.35.
 3. The dovetail structure of the fan asclaimed in claim 1, wherein the sub engagement portion is constituted bya projection portion which is provided in an inner end portion of aforward end of the fan, and has an outer peripheral surface spaced at afixed distance R from the axis of the rotating shaft, and the spin conehas a concave groove having an inner peripheral surface fitted to anouter peripheral surface of the projection portion, and a faucet portionfitted to a cylindrical inner surface provided in the disc.
 4. Thedovetail structure of the fan as claimed in claim 1, wherein the subengagement portion is constituted by a plurality of slope dovetailportions extending at a fixed angle with respect to the axis of therotating shaft from the leading edge of the fan to the intermediateportion, and spaced at a fixed angle in a peripheral direction, and thespin cone has a plurality of slope dovetail grooves fitted to the slopedovetail portions, and a faucet portion fitted to the cylindrical innersurface provided in the disc.
 5. The dovetail structure of the fan asclaimed in claim 1, wherein the sub engagement portion has a pluralityof parallel dovetail portions extending in parallel to the axis of therotating shaft from the leading edge of the fan to the intermediateportion, and spaced at a fixed angle in a peripheral direction, and thespin cone has a plurality of parallel dovetail grooves fitted to theparallel dovetail portions, and a faucet portion fitted to thecylindrical inner surface provided in the disc.
 6. The dovetailstructure of the fan as claimed in claim 1, wherein the sub engagementportion is constituted by a plurality of expanded portions extendingfrom the leading edge of the fan to the intermediate portion and spacedat a fixed angle in a peripheral direction, and the spin cone has aplurality of fitting grooves fitted to a front lower edge of the fan inan upper portion than the expanded portions, and a faucet portion fittedto the cylindrical inner surface provided in the disc.